The　exploitation　of　high-performance　nonlinear　optical　(NLO)　materials　is　necessitated　by　the　broad　application　of　ultra-intensive　and　ultra-fast　lasers.　The　superb　nonlinear　absorption　and　electronic-structure-related　NLO　response　of　M3HHTP2　are　introduced　here,　where　M　is　Co(II),　Ni(II),　or　Cu(II)　and　HHTP　is　2,3,6,7,10,11-hexahydroxytriphenylene.　With　the　laser　excitation　at　532 nm,　the　Cu3HHTP2　exhibits　a　two-photon　absorption　(2PA)　cross-section　of　1.38　±　0.11 ×　107　GM,　a　value　much　larger　than　those　of　most　reported　NLO　materials　so　far.　The　NLO　response　of　M3HHTP2　correlates　strongly　with　the　number　of　metal　d　electrons.　With　metal　d　electrons　number　increasing　from　7　to　10,　the　optical　nonlinearity　of　M3HHTP2　under　the　laser　excitation　at　532 nm　varies　from　three-photon　absorption　(3PA)　in　Co3HHTP2,　a　combination　of　3PA　and　2PA　in　Ni3HHTP2,　to　2PA　in　Cu3HHTP2.　Abundant　metal　d　electrons　can　mitigate　the　ground-state　depletion,　and　therefore　the　2PA　is　enhanced.　Accordingly,　the　superb　nonlinear　absorption　of　Cu3HHTP2　can　be　associated　with　abundant　d　electrons　in　Cu.　©　2021　Wiley-VCH　GmbH